The invention concerns a fluid-powered percussion tool with a percussion piston movable within a working cylinder and impacting with a tool, as well as a control, comprising a control valve that moves relative to a housing, wherein the percussion piston has two piston areas of variable size, of which the smaller piston area that is effective in the direction of the return stroke is constantly connected to a pressure line under operating pressure and the larger piston area that is effective in the direction of the working stroke is connected via the control alternately to the pressure line and a discharge line. The control valve comprises two valve faces effective in opposite direction, which are designed and admitted with pressure, such that the control valve switches to the working stroke position when the percussion piston approaches the upper dead point during the return stroke, in which position the operating pressure is also present at the larger piston area, and that the control valve changes to the return stroke position when the percussion piston approaches the point of impact during the working stroke, in which position the admitting of the larger piston area with operating pressure is interrupted and a connection is established with the discharge line.
A fluid-powered percussion tool of the aforementioned type is disclosed in the German patent document DE-C2-34 43 542. The control valve of the known device has two valve faces of different size that are effective in opposite movement direction, of which the smaller valve face that affects the control valve in the return stroke position is constantly connected to the pressure line and of which the larger valve face is connected in each case as a control surface via a control line and a circumferential groove between the piston areas, but only at times as well as alternately with the pressure line or an non-pressurized return line.
The use of a special holding or shuttle valve, which is installed in the control line that operates jointly with the control and which is alternately also connected to the return line, is designed to ensure that even with a reflection of impact energy via the tool onto the percussion piston, this reflected energy is recovered hydraulically, thereby resulting in an increase in the number of impacts for the percussion piston. The control itself is arranged separate from the working cylinder holding the percussion piston.
A hydraulically operated percussion tool with a percussion piston is also known from European patent document EP-A1-0 149 967, where a hydraulic reset force is also effective in the direction of the return stroke by way of a smaller piston area. The associated control, which is integrated into the working cylinder holding the percussion piston, has a control valve in the form of a sleeve-type switching element. This control valve encloses with a clearance the percussion piston in the region of the rear cylinder chamber segment, which can be used to admit a larger piston area that is effective in the direction of the working stroke with working pressure. For this known embodiment, the control valve is moved mechanically, by means of the percussion piston from the return stroke to the working stroke position. Accordingly, the hammer-piston stroke cannot be changed.
In contrast to the last-mentioned document, German patent document DE-C2-30 23 600 describes a hydraulic impact rotary drilling machine with a sleeve-type control valve design, which is controlled hydraulically via the percussion piston and is supported movably on the percussion piston as well as on the inside of the working cylinder. This known impact rotary drilling machine has the disadvantage of requiring a double fitting in the control valve region, meaning the control valve must have very little play in the outside and inside diameter region to ensure a perfect operation.